Phosphagens

Phosphagens are a class of energy-storage compounds used by many animals, some protists, and certain invertebrates to store and rapidly mobilize high-energy phosphate groups. They function as short-term ATP buffers that enable quick regeneration of ATP from ADP during phases of high or fluctuating energy demand.

The core chemical principle is a reversible transfer of a phosphate group between a phosphagen and ADP, catalyzed by specific phosphagen kinases. In vertebrates, the principal phosphagen is phosphocreatine (creatine phosphate) and its kinase is creatine kinase. In many invertebrates, arginine phosphate (phosphoarginine) serves a similar role, with arginine kinase as the enzyme. Other phosphagens described in various taxa include lombricine phosphate, taurocyamine phosphate, and glycocyamine phosphate, each paired with its respective kinase.

Physiological roles include rapid ATP regeneration during onset of muscular activity, buffering of cellular energy status, and facilitation of intracellular energy transport. By providing a quick source of high-energy phosphate, phosphagens help sustain muscle contraction and other energy-demanding processes until oxidative phosphorylation or glycolysis can meet ongoing needs.

Distribution and evolution of phosphagen systems vary among lineages, reflecting adaptations to different metabolic strategies. Creatine kinase/phosphocreatine systems are widespread in vertebrates, while arginine kinase/phosphoarginine systems are common in many invertebrates. The diversity of phosphagens illustrates how organisms optimize energy management for specific ecological and physiological demands.